Automotive vehicles often use vacuum fluorescent displays (VFDs) as instrumentation for providing vehicle speed and other information to the operator. The display is housed in a vacuum tube having a lead frame defining pins connected to various anode portions. In external control circuitry, typically speed data, various switch states, fuel level, dimmer control, and other digital or analog information is fed to a microprocessor which determines which anode portions should be illuminated to convey the information in an orderly manner. Many outputs are then coupled from the microprocessor to the pins via drivers which supply the required voltage level for the desired illumination intensity.
Generally such VF displays use fixed segment anodes to display graphic data. Each anode sement, which comprises one of the individual graphic segments when activated, is connected via a lead frame pin of the VFD the the external control circuitry which is physically separate from the display. This control circuitry is effective to impose the correct "on" voltage on each anode segment to be illuminated and an "off" voltage on the remaining segments. Such fixed segment displays are generally dedicated to specific information, so that a large array of such displays would be required to afford all the information which might be desirably provided to the operator. In the case of direct viewing of the display, limitations in instrument panel space prohibits such expanses of display area. Moreover, when the display is used in conjunction with a head up display (HUD), very small displays are required to minimize the HUD package size. A limiting factor in VFD package size reduction is the number of lead frame pins for connection to the outside circuit device. In practice, the anode segments are multiplexed (and thus less bright) to reduce the number of VF driver outputs required and/or to reduce the number of pins to keep the package size smaller.
To show a large amount of information in a small display space it has been proposed to utilize a reconfigurable display which is capable of revealing several types of information on a time sharing basis. It is known to use conventional dot matrix displays for this purpose but these have had limited brightness due to multiplexing requirements. Heretofore such displays have driven by pinning out each row and column of the array to a lead frame for connection to external driving circuitry. Each row or column uses two pins so that, for example, a 40.times.64 pixel array requires more than 200 pins, thereby limiting size reduction attempts.
An improvement over the conventional dot matrix display in terms of brightness is the active matrix vacuum fluorescent display (AMVFD) which includes a silicon substrate containing pixel and display multiplexing circuitry. By sending the appropriate data to the device data lines and power supply lines, the pixels on the device are turned on or off. A variety of reconfigurable graphics such as characters, numbers, ISO symbols, map data, etc. can be displayed. The construction of such AMVFDs comprises an evacuated glass envelope having a mounting surface bearing the silicon substrate and conductive traces extending across the mounting surface from the substrate to a lead frame which affords connections to external circuitry. Wire bonds couple the conductive traces to the silicon substrate. Filaments necessary to VFD operation are also included within the envelope. Self standing grids are not needed since a coplanar grid on the anode surface is employed. Details of such displays are disclosed in the papers "MOS-Addressed VFD Character Display Incorporating Static RAM", Uemura et al, SID 85 Digest, 362 and "High-Resolution VFD On-a-Chip", Yoshimura et al, SID 86 Digest, 403, which are incorporated herein by reference. Disadvantages of the AMVFD are the high cost of the silicon substrate and the need for individual pins for each row and column, as in the conventional dot matrix display. It is desirable, however to obtain the advantages of the AMVFD in a smaller size and at a lower cost.